Low friction lubrication assembly

ABSTRACT

[Object] A low friction assembly is desired. 
     [Solving Means] The present invention relates to a new low-friction lubrication assembly comprising a first member relatively slidable against a second member, the first member having chemical affinity with an OH-group on its sliding surface; and one or more oxygen containing compounds, provided on the sliding surface of the first member and being able to produce a tribofilm attached to the sliding surface of the first member through hydrogen bond interactions. Preferably the second member comprises a similar OH-terminated sliding surface wherein an oxygen containing compound (lubricant)-supported interface between the first and second sliding surfaces results in a H- and/or OH-terminated interface developing repulsive forces thereinbetween.

TECHNICAL FIELD

The present invention relates to a low-friction lubrication assemblycomprising at least first and second members, the surfaces or coatingsthereof are in sliding contact with each other such that under presenceof at least one friction reducing agent (oxygen containing compound) aspecific and unique tribofilm develops comprising hydrogen and/orhydroxyl groups.

BACKGROUND ART

In the present state of the art, low friction under lubricated tests isgenerally attainable through the formation of CH₃-terminated tribofilmsor in the presence of solid lamellar compounds such as MoS₂ or boricacid, for example. However, almost typical friction coefficientsobtained are not lower than 0.04 and lower than 0.1, and thereforevalues lower than 0.04 have hardly been reported so far.

Global environmental problems such as global warming and ozone layerdestruction are coming to the fore. As it has been said that the globalwarming is significantly affected by CO₂ emission, the reduction of CO₂emission, notably the setting of CO₂ emission standards, has become abig concern to each country. One of the challenges to reduce CO₂emission is to lower an energy loss due to friction loss of machines,facilities and the like, particularly to improve vehicle fuel efficiencyor fuel economy that depends on the performance of engine slidingmembers and a lubricating oil applied thereto. There are the followingapproaches to improve the vehicle fuel efficiency: (1) lowering theviscosity of the lubricating oil, thereby reducing viscous resistance inhydrodynamic lubrication regions and agitation resistance in the engine;and (2) adding a suitable friction modifier and other additives into thelubricating oil so as to reduce friction losses under the conditions ofmixed lubrication and boundary lubrication.

A patent literature 1 discloses a low-friction sliding member with abase material having a surface and a hard carbon thin film formed on atleast a part of the surface of the base material, wherein a tribofilmhaving at least one functional group selected from the group consistingof an ether linkage, an oxido and a hydroxyl group is formed on the hardcarbon thin film when the hard carbon thin film is in slidable contactwith an opposite member in the presence of an organic oxygen-containingcompound.

The patent literature 1: European Patent No. 1510594A specification

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention

The present invention aims to suggest a low-friction lubricationassembly showing improved sliding characteristics over low frictionassemblies shown in the art.

Means for Solving the Problems

The problem is solved with a low friction assembly comprising:

a first member relatively slidable against a second member, the firstmember having chemical affinity with an OH-group on its sliding surface;and

one or more oxygen containing compounds located on the sliding surfaceof the first member and being able to produce a tribofilm to be locatedon the sliding surface of the first member having the chemical affinity,through hydrogen bond interactions with the OH-group.

The Best Mode for Carrying out the Invention

Hereinafter, a low friction assembly of the present invention will bediscussed in detail.

As discussed above, the low friction assembly of the present inventioncomprises:

a first member relatively slidable against a second member, the firstmember having chemical affinity with an OH-group on its sliding surface;and

one or more oxygen containing compounds located on the sliding surfaceof the first member and being able to produce a tribofilm to be locatedon the sliding surface of the first member having the chemical affinity,through hydrogen bond interactions with the OH-group.

Essential is the creation of a hydrogen bond interaction between a H orOH-terminated surface of the first member and specific polar moleculespresent in an oxygen containing compound (lubricant) which can begaseous or liquid. In particular, said hydrogen bonding interaction, onthe one hand, and the oxygen containing compound (lubricant) determinedH-terminated surfaces of the first and/or second member, on the otherhand, serve to establish a unique low-friction lubrication assembly orsystem which allows to reduce friction values to the range of frictioncoefficient below 0.04 and in specific cases below 0.01.

On other words, in a two-way mechanism the tribochemical reaction of thesurface atoms such as C, Al, Si, etc of the first and/or second memberwith the hydroxyl groups present in the molecules of the oxygencontaining compound (lubricant) occurs and thereafter the oxygencontaining compound (lubricant) molecules adsorb on that OH-terminatedsurface by hydrogen bonding. Thus the newly created friction interface(including the oxygen containing compound (lubricant)) is either anH-terminated surface or a mixed OH— and/or H-terminated surface whereinany amount of more than 50% OH may be beneficial over a purelyH-terminated surface.

In case of biological material, for example as a second member, proteinscomprising for example OH- and SH-groups, may organize on the OH- orH-terminated surface of the first member.

In a preferred embodiment, the second member further comprises ahydroxyl group on the sliding surface, preferably an OH-terminatedsliding surface, and the tribofilm is also attached to the slidingsurface of the second member through hydrogen bonding in response to asliding movement. Further, the first member comprises preferably atleast one selected from the group consisting of an amorphous materialand a crystallized material.

In a further preferred embodiment the first member comprises at leastone selected from the group consisting of Si, SiO₂, Al₂O₃, Si₃N₄, MgO orany single metal or mixed metal combination of oxides, nitrides andcarbides (for example silicon carboxide, oxynitride and carbonitride)and more generally a material formed of elements having a chemicalaffinity and propension to form hydroxides compounds (for example Metal(OH)x). Which ever its chemical composition and crystal structure, thefirst sliding member can also be coated with a diamond and diamond-likecarbon.

The diamond-like carbon contains preferably hydrogen in an amount of notmore that 10 atomic %, more preferably the diamond-like carbon is formedof diamond-like carbon of a-C type or ta-C type containing substantiallyno hydrogen.

The second member comprises preferably at least one selected from thegroup consisting of an amorphous material and a crystallized material.

In a further preferred embodiment, the second member is formed of thesame materials as those (as listed above) of the first member, orcomprises at least one selected of the group consisting of C, Fe, Al,Mg, Cu, Fe alloy, Al alloy, Mg alloy and Cu alloy.

Preferably, the oxygen containing compound (friction modifier orlubricant) has at least one hydroxyl group in its chemical formulae.

Further, the oxygen containing compound comprises preferably at leastone of the group consisting of an alcohol, a carboxylic acid, an ester,an ether, a ketone, an aldehyde and a carbonate, and/or a derivative ofat least one of the group consisting of an alcohol, a carboxylic acid,boric acid, an ester, an ether, a ketone, an aldehyde and a carbonate.

In a further preferred embodiment, the oxygen containing compoundcomprises at least one selected from the group consisting of polyalpha-olefin (PAO), glycerol monooleate (GMO), glycerol, H₂O andperoxides, more preferably the oxygen containing compound comprises H₂O₂or a mixture of H₂O and H₂O₂, in particular H₂O₂. In another preferredembodiment the oxygen containing compound (lubricant) is glycerol. Instill another preferred embodiment, the oxygen containing compound(lubricant) is found in synovial liquid, in particular lubricin-OH. In afurther preferred embodiment the oxygen containing compound (lubricant)is PAO-ester.

In a further preferred embodiment, the oxygen containing compoundcomprises polyalcohols which include at least one selected from thegroup consisting of inositol, pyrogallol, urushiol, pyrocatechol,resorcinol, hydroquinone, fullerenol, penthaerythritol, othersaccharides, their isomers, derivatives and substitution compounds.Examples of the above-mentioned saccharides are agarose, adenosinetriphosphate, apiose, amylase, amylopectin, sugar glass, arabinoxylan,alkylglycoside, alginic acid, sodium alginate, aldaric acid, aldose,altrose, aldonic acid, arbutin, allose, idose, inulin, uronic acid,erythritol, erythrose, oligosaccharide, carrageenan, galactose,carboxymethyl cellulose, reducing sugar, xanthan gum, rare sugar, xylan,xylitol, xylulose, xylose, cycloglucan, chitin, chitosan, guar gum,glycogen, glycosaminoglycan, glycosyl group, glyceraldehyde,glucuronoxylan, glucuronolactone, glucuronic acid, glucosamine, glucose,glucomannan, gluconic acid, gulose, ketose, kerato sulfate, gentiobiose,collodion, chondroitin, chondroitin sulfate, saponin, digitonin,cycloawaodorin, cyclodextrin, cytidylic acid, sinigrin, dihydroxyacetone, starch nitrate, cane sugar, GF2, sucralose, sucrose, refinedsugar, cellulose, cellulose ester, cellobiose, thickening agent,sorbitol, sorbose, tagatose, polysaccharide, talose, monosaccharide,deoxyribose, dextrin, dermatan sulfate, invert sugar, starch, sugaralcohol, glycoprotein, threose, trehalose, nicotinamide adeninedinucleotide phosphate, nicotinamide adenine dinucleotide, disaccharide,glycoside, hyaluronic acid, fucoidan, fucose, psicose, ptaquiloside,fructose, pectin, heparin, hemicellulose, maltose, mannitol, mannose,lactose, rhamnose, lyxose, ribulose, ribose, rutin and the like.

In a further preferred embodiment, the oxygen containing compoundcomprises a mixture of at least one of the above-listed polyalcohols andglycerol.

In a further preferred embodiment, the oxygen containing compoundcomprises a mixture of at least one of the above-listed polyalcohols andH₂O.

Preferably, the oxygen containing compound is liquid or gaseous,nanoparticles or thin organic deposited films by any availabledeposition techniques (Langmuir Blodgett films for example).

Preferably, the sliding surface of the first member is subject topretreatment before being slid against the second member.

Contaminants (contamination substances) such as fats and oils and thelike will be felt uneasy particularly in processing (high precisionprocessing) for precision machines or in precision machines per se;however, such contaminants cannot be present if volatile substances suchas H₂O₂, alcohol or the like is used as the oxygen containing compound(lubricant). Accordingly, it will be understood that the oxygencontaining compound is effective for the sliding action (sliding action,for example, in a step of removing a metal die) in a processing step forprecision machines such as “watches” and the like, or effective forsliding sections of the precision machines. The oxygen containingcompound tends to easily volatilize particularly in cold and warmclimates thereby being optimum in contaminant preventing effect. Theabove-mentioned high precision processing includes a cold processing anda warm processing. The cold processing is a plastic working at atemperature lower than a recrystallization temperature of a metal. Thewarm processing is a plastic working upon heating a metal material in atemperature range lower than the recrystallization temperature.

Preferably, said pretreatment comprises cleaning; mechanical activation,in particular polishing with specific agent such as H₂O₂; chemicaltreatment, in particular by application of H₂O₂ after physical treatmentby laser or electron beam treatment.

Preferably, the sliding surface of the first member is hydrogen-freebefore application of the oxygen containing compound (OH groupcontaining lubricant) and establishing sliding contact to the secondmember but build an OH-terminated sliding surface upon entering intosliding contact with the second member, under preceding or simultaneousapplication of the above-mentioned oxygen containing compound (OH groupcontaining lubricant) on the sliding surface of the first member.

The low-friction lubrication assembly of the present invention issuitable for any application wherein very low friction between twomembers is desired. The assembly can for example be used in the field ofmechanics, physics or medicine. In particular, the assembly is suitablefor use in a combustion engine, medical devices (endoscope, catheter,syringe, needle, blood collection tube, medical electronic pump and thelike), micromechanical devices, and nanomechanical devices (MEMS; MicroElectromechanical System, NEMS; Nano Electromechanical System,particularly precision machines such as watches or the like), and otherlow friction requiring systems (shavers, compressors, pumps, gears,bearings and the like). Additionally, tools to be used for machining mayencounter a problem in which friction and adhesion occur not only incutting sections but also at the face and flank thereof due to cuttingpieces rolled in; however, by virtue of these low friction assemblies,reduction in driving force during the machining can be expected while atool life can be largely extended owing to preventing the adhesion.

Regarding the first and second members of the new low friction assembly,a wide variety of materials and combinations is given. Accordingly, thepresent invention is primarily focused on determining the first memberwhile the second member can reach from biological material, such as forexample considering the lubrication assembly being formed by a medicineendoscope and the skin surface of the human body or the surface of innervessels of the human body up to applications where metals or metalcoated surfaces slide on each other such as, machine tooling or enginedesign, such as sliding components in internal combustion engines.Preferably, at least the first member comprises a smooth surface, saidsurface being comprised of a thin layer coating such as DLC coating onmetal or semi-metal comprising base materials.

The low friction properties of the new system are considered to be basedon the unique combination of a sliding surface of the first membercomprising an OH-terminated surface, at least after having been incontact with an oxygen containing compound (OH-group containinglubricant), said OH-terminating surface being able to establish hydrogenbonding with a gaseous or liquid lubricant, such as glycerol. TheOH-terminated sliding surface is adapted to oppose an OH-terminatedopposite surface either established by the lubricant deposition ofOH-group on the sliding surface of the second member or the slidingsurface of the second member itself establishing an interactive hydrogenbond between the OH-terminated sliding surface of the first and secondmember and the OH-groups of the oxygen containing compound (lubricant).Preferably, DLC coatings are being used on the side of the first member.

Preferably, there will be a pretreatment of the sliding surface of atleast the first member to reduce roughness and install OH hydroxylgroups on the polished surface.

Hereinafter, the present invention is explained in further detail bymeans of several embodiments thereof in conjunction with theaccompanying drawings.

In FIGS. 1 and 2, the new surface chemistry (called OH-tribofilm) isformed on both sliding surfaces by a tribochemical reaction between thematerials of the first and second members and the oxygen containingcompound (lubricant) present therebetween during sliding of the firstand second members. Alternatively, it can be formed by a pre-treatmentof the surface before use, “pre-treatment” can be chemical, vacuumassisted cleaning and reaction with specific agents and even mechanicalpolishing in the presence of the agents or a combination of the three.

Such treatment can be of mechanical (polishing), chemical ormechanochemical (H₂O₂), or other cleaning or physical nature (electronor ion bombardment) all intended for activating atoms present at thesliding surface.

Preferably, the thickness of the OH-tribofilm is usually in thenanometer range and the OH-tribofilm has a termination made both ofhydroxyl groups (OH) and H atoms but even more preferably thetermination is made of OH-atoms. It is much preferable to have more than50% of OH groups on the surface. Even more favorable is 100% of OHgroups.

The OH-tribofilm can advantageously form hydrogen bonding with variousmolecules such as alcohols, esters, ethers, acids, amines, imides,thiols, peroxides and water, and others (boric acid for example).Generally, all molecules susceptible to have hydrogen bonding with watercan be candidates.

The termination of the OH-tribofilm with the hydrogen bond-attachedmolecules has preferably a H-terminated surface.

It has been confirmed that the friction between such H-terminated and OHterminated surfaces is extremely low due to the repulsive forces betweenpositively charged hydrogen atoms. Because of the electronegativity ofoxygen atoms, the OH-terminated surface is even more repulsive.

The OH-tribofilm is continuously re-formed if it is needed by thetribochemical reaction.

Due to hydrogen termination between the two sliding surfaces formed bythe oxygen containing compound (lubricant) in between, repulsive forcesare formed in between the contacting sliding surfaces, the first andsecond member which is even increased in case of hydroxyl grouptermination between the two sliding surfaces which is also preferred inview of a high flexibility of a COH-bonding with the OH compound beingfree to rotate around a C—O bond to assume a stationary position. Ascompared with well known “OH-terminated surface” having a high surfaceenergy and the property of being not wetted with water within hydrogenbond, “C—OH terminated surface” has a low surface energy and theproperty of tending to be wetted with water. The reason for this issupposed that “C—H terminated surface” is very strong, and “H” of “C—Hterminated surface” cannot form a hydrogen bond with a water moleculeunder steric hindrance. In this regard, in the hydrogen bond of “C—H—O”,it is preferable that three atoms are generally in alignment with eachother. In contrast, as shown in FIG. 7, “C—O—H terminated surface” ofta-C has a considerable degree of freedom because C—O bond is rotatable,and therefore the position of water molecule (H—O—H) capable of beingformed by hydrogen bond with OH group of glycerol at the surface isoptimized so as to readily form hydrogen bond.

Preferably, glycerol is used as the oxygen containing compound(lubricating agent) and, due to having 30H groups and capable of havingthree hydrogen bonds per module, allows the molecule to stay longer on aOH terminated surface but having some repulsiveenergy as C—O and C—Cbonds are free to rotate around their axle. A glycerol lubricatingsystem can optimize its configuration to have better hydrogen bondingsituations considering the different bonding forces in view of thepreferred alignment of O—H—O groups. Generally, H-terminated surfacesbetween the first member and the oxygen containing compound (lubricant)and/or between the first and second members appear to be more preferablethan the provision of OH-terminated surfaces.

In preferred embodiments of the present invention the first member has acoating of a hydrogen free amorphous carbon layer (a-C) or a hydrogenfree tetrahedral carbon layer (ta-C). The second member has preferablyalso a coating of a hydrogen free amorphous carbon layer (a-C) or ahydrogen free tetrahedral carbon layer (ta-C). Particularly preferredare the following combinations of first and second members: a-C coatingand a-C coating; ta-C coating and a-C coating; a-C coating and ta-Ccoating; ta-C coating and ta-C coating. Particularly preferred basematerials on which to apply these coatings are SCM415 (carburization) orheat treated SUJ2. The above-mentioned a-C and ta-C are respectivelylocated in ranges shown in a ternary state diagram of FIG. 8.

A preferred oxygen containing compound (lubricant) for these members isglycerol.

The hydrogen-free carbon layer such as DLC reacts with OH-groups of theoxygen containing compound (lubricant) immediately upon contact with theoxygen containing compound (lubricant). This leads to the formation ofan OH-terminated sliding surface.

FIG. 3 represents a model of the new low-friction lubrication assemblycomprising a 100% H-terminated surface of the first and second member,wherein the repulsive affinity therebetween drastically reduces afriction coefficient. This will be apparent from FIG. 4 which isexperimental data shows performances of a hydrogen-free DLC(substantially containing no hydrogen; ta-C) and hydrogen-free DLCsystem using a glycerol lubrication. Alternatively, the frictioninterface along the dotted line between the first and second members inFIG. 2 may also comprise OH-groups to establish a mixture of H- andOH-termination of the surfaces of the first and second members, thusforming a repulsive interface between the H- and/or OH-terminatedsurfaces of the opposite members upon relative sliding of same withrespect to each other.

With DLC and other materials of interest in particular as the first andsecond members, a two-steps mechanism is provided: first the creation ofan OH-terminated surface based on the tribochemical reaction of surfaceatoms of the members, such as C, Se, Si, etc. with the hydroxyl groupspresent in the members of the oxygen containing compound (lubricant).Then the molecules of the oxygen containing compound (lubricant) mayadsorb on that crated OH-terminated surface by hydrogen bonding creatinga new friction interface of the first and/or second member comprising anH- and/or OH-terminated surface is developed. Thus, repulsive forcesalong said interface facilitate a new type of low friction lubricatedassembly to be created.

Hereinafter, the present invention will be discussed with reference toExamples and Comparative Examples; however, the present invention is notlimited to these Examples.

EXAMPLES 1 TO 9 AND COMPARATIVE EXAMPLES 1 TO 4

Plates and pins shown in Table 2 were produced respectively by formingcoatings on base materials thereof. Respective produced plates and pinshad respectively film thicknesses, surface roughnesses and surfacehardnesses as shown in Table 2, similarly.

(Vibration Friction Wear Test (SRV Friction Test))

The obtained plate and pin were set on a vibration friction wear testingmachine produced by Optimol Instruments Prüftechnik GmbH, upon which theplate and pin were wetted with a lubricating oil (oil) and underwent avibration friction wear test (SRV (pin-on-plate) friction test) therebymeasuring a friction coefficient. An obtained result is also shown inTable 2.

FIG. 6 is a perspective explanatory view showing the manner of thevibration friction wear test (SRV (pin-on-plate) friction test). Asshown in this figure, the pin is located on the plate, upon which thepin slidingly moves in a reciprocating manner on the plate. A verticalarrow A indicates a load direction (the upper side to the lower side;vertical direction), and a horizontal arrow indicates a direction(horizontal direction) in which the pin slides on the surface of theplate.

TABLE 1 Experiment with Glycerol Test condition Maximum hertzian contactpressure 270 MPa Temperature 80° C. Amplitude 3 mm Number of vibration50 Hz Test time 15 minutes

TABLE 2 Examples/Comparative Examples with Glycerin Sliding members forpin-on-disc friction test Film thickness Surface hardness Surfaceroughness Ra disc pin [μm] [Hv] [μm] lubricating Friction Example bacematerial coating bace material coating disc pin disc pin disc pin oilcoefficient EX. 1 SCM415 a-C Heat treated a-C 0.7 1.1 1500 1600 0.030.03 Glycerin 0.009 (carburization) SUJ2 EX. 2 SCM415 a-C heat treateda-C 0.8 1.8 1600 1800 0.03 0.03 Glycerin 0.008 (carburization) SUJ2 EX.3 SCM415 a-C heat treated a-C 0.8 0.9 1600 1500 0.05 0.05 Glycerin 0.008(carburization) SUJ2 EX. 4 SCM415 a-C heat treated ta-C 0.9 0.9 16002800 0.05 0.05 Glycerin 0.008 (carburization) SUJ2 EX. 5 SCM415 ta-Cheat treated ta-C 1.1 0.9 2900 2800 0.04 0.05 Glycerin 0.007(carburization) SUJ2 EX. 6 SCM415 ta-C heat treated ta-C 1.1 0.8 29002700 0.05 0.02 Glycerin 0.007 (carburization) SUJ2 EX. 7 SCM415 ta-Cheat treated ta-C 0.9 1.1 2800 2900 0.05 0.03 Glycerin 0.007(carburization) SUJ2 EX. 8 WC—Co ta-C heat treated ta-C 0.3 0.9 28003500 0.05 0.10 Glycerin 0.007 (super hard alloy) SUJ2 EX. 9 WC—Co ta-Cheat treated ta-C 0.7 0.3 3200 2900 0.05 0.04 Glycerin 0.007 (super hardalloy) SUJ2 Comp. Ex. 1 SCM415 a-C heat treated none 0.8 1600 750 0.100.03 Glycerin 0.02 (carburization) SUJ2 Comp. Ex. 2 SCM415 ta-C heattreated none 0.8 2700 750 0.04 0.03 Glycerin 0.03 (carburization) SUJ2Comp. Ex. 3 SCM415 ta-C heat treated ta-C 0.8 1.1 2700 2900 0.10 0.035W-30 0.06 (carburization) SUJ2 engine oil Comp. Ex. 4 SCM415 None heattreated none 710 750 0.05 0.03 5W-30 0.14 (carburization) SUJ2 engineoil

In further preferred embodiments of the present invention the firstmember is made of steel, DLC coated steel or Al₂O₃. Preferably, thesecond member is also made of steel, DLC coated steel or Al₂O₃.Particularly preferred are the following combinations of first andsecond members: steel and Al₂O₃; DLC/steel and Al₂O₃; DLC/Al₂O₃ andDLC/Al₂O₃; steel and steel; Al₂O₃ and Al₂O₃; Al₂O₃ and DLC/Al₂O₃;DLC/steel and steel; DLC/Al₂O₃ and steel; DLC/steel and DLC/steel.

A preferred lubricant for these members is glycerol. The following Table3 contains experimental data for a combination of glycerol as lubricantwith members made of steel, DLC coated steel and Al₂O₃.

TABLE 3 Glycerol lubrication Contact Sliding Mean Plate or pressurespeed friction Ball or pin disc (MPa) (mm/s) (μ) Δμ Wear Steel Al₂O₃ 3951 0.04 ±0.03 No measurable * DLC/Steel Al₂O₃ 395 1 0.06 ±0.005 Tribofilm(200 nm) DLC/Al₂O₃ DLC/Al₂O₃ 727 1 0.06 ±0.02 Wear (200 nm) (200 nm)(Removal of the coating) Steel 340 1 0.22 ±0.005 Wear * The term “Nomeasurable” in Table 3 refers to a “tribofilm thickness being below 10nm, which cannot be observed by eyes or even conventional opticalmicroscopy.

A further preferred oxygen containing compound (lubricant) for thesemembers is PAO-ester. The following Table 4 contains experimental datafor a combination of PAO-ester as the oxygen containing compound(lubricant) with members made of steel, DLC coated steel and Al₂O₃.

TABLE 4 PAO-Ester lubrication Contact Sliding Mean Plate or pressurespeed friction Ball or pin disc (MPa) (mm/s) (μ) Δμ Wear Steel Al₂O₃ 3951 0.075 ±0.025 No visible DLC/Steel Al₂O₃ 395 1 0.05 ±0.005 Brown (900nm) Tribofilm * DLC/Al₂O₃ DLC/Al₂O₃ 725 1 0.05 ±0.001 Wear (200 nm) (200nm) (Removal of the coating) DLC/Steel DLC/Steel 548 2-3 0.08 ±0.01Hardly (20 AP) (20 AP) visible The combination of DLC/Steel and Al₂O₃with the lubricant PAO-ester is particularly preferred. * The term“Brown Tribofilm” in Table 4 refers to “film, being visible by opticalmicroscopy”.

FIG. 5 is an experimental data in case of the above-mentionedhydrogen-free DLC and hydrogen-free DLC system using a gaseous H₂O₂lubrication, in which the friction coefficient is drastically lowered.

In case of using PAO-ester or glycerol lubrication, the frictioncoefficient is largely lowered even in a ruby (Al₂O₃)/hydrogen-free DLCsystem. This is apparent from FIG. 9 and FIG. 10. FIG. 9 is anexperimental data showing the performance of the ruby(Al₂O₃)/hydrogen-free DLC system using the glycerol lubrication. FIG. 10is an experimental data showing the performance of the ruby(Al₂O₃)/hydrogen-free DLC system using the PAO-ester lubrication.

Additionally, in case of using PAO-ester or glycerol lubrication as sameas the above, the friction coefficient is largely lowered even in a ruby(Al₂O₃)/steel (Fe; iron) system. This is apparent from FIG. 11 and FIG.12. FIG. 11 is an experimental data showing the performance of the ruby(Al₂O₃)/steel system using the glycerol lubrication. FIG. 12 is anexperimental data showing the performance of the ruby (Al₂O₃)/steelsystem using the PAO-ester lubrication.

Hereinafter, technical bases of the present invention derived from theabove-discussed embodiments will be discussed.

(1) A low-friction lubrication assembly comprising: a first memberrelatively slidable against a second member, the first member havingchemical affinity with an OH-group on its sliding surface; and one ormore oxygen containing compounds located on the sliding surface of thefirst member and being able to produce a tribofilm to be located on thesliding surface of the first member having the chemical affinity,through hydrogen bond interactions with the OH-group.

(2) A low-friction lubrication assembly as described in (1), wherein thesecond member further has chemical affinity with an OH group, and thetribofilm is also able to be formed on a sliding surface of the secondmember through hydrogen bond interactions with the OH-group in responseto sliding motion.

(3) A low-friction lubrication assembly as described in (1), wherein atleast one OH group termination is provided onto the sliding surface inthe first member after a certain sliding motion.

(4) A low-friction lubrication assembly as described in (1) or (3),wherein the tribofilm is formed to be located on the sliding surface ofthe first member through hydrogen bond interactions between at least oneOH termination provided to the surface of the first member and an OHgroup in the oxygen containing compound.

(5) A low-friction lubrication assembly as described in any of (1) to(4), wherein at least one OH group termination is further provided ontothe sliding surface of the second member after a certain sliding motion.

(6) A low-friction lubrication assembly as described in (1) to (5),wherein the tribofilm is further formed to be located on the slidingsurface of the second member through hydrogen bond interactions betweenat least one OH termination provided to the surface of the second memberand an OH group in the oxygen containing compound.

(7) A low-friction lubrication assembly as described in any of (1) to(6), wherein the first member comprises at least one selected from thegroup consisting of an amorphous material and a crystallized material.

(8) A low-friction lubrication assembly as described in any of (1) to(7), wherein the first member comprises at least one selected from thegroup consisting of Si, SiO₂, Al₂O₃, Si₃N₄, MgO or any single metal ormixed metal combination of oxides, nitrides and carbides.

(9) A supper low-friction lubrication assembly as described in any of(1) to (8), wherein the first member comprises at lease one selectedfrom the group consisting of silicon carboxide, oxinitride andcarbonitride, a material formed of elements having a chemical affinityand tendency to form hydroxides (for example Metal (OH)x), diamond anddiamond-like carbon.

(10) A low-friction lubrication assembly as described in (8) or (9),wherein the diamond-like carbon contains hydrogen in an amount of notmore that 10 atomic %.

(11) A low-friction lubrication assembly as described in (10), whereinthe diamond-like carbon is formed of diamond-like carbon of a-C typecontaining substantially no hydrogen or diamond-like carbon of ta-Ctype.

(12) A low-friction lubrication assembly as described in any of (1) to(11), wherein the second member comprises at least one selected from thegroup consisting of an amorphous material and a crystallized material.

(13) A low-friction lubrication assembly as described in any of (1) to(12), wherein the second member comprises at least one selected from thegroup consisting of Si, SiO₂, Al₂O₃, Si₃N₄, MgO or any single metal ormixed metal combination of oxides, nitrides and carbides.

(14) A supper low-friction lubrication assembly as described in any of(1) to (13), wherein the second member comprises at lease one selectedfrom the group consisting of silicon carboxide, oxinitride andcarbonitride, a material formed of elements having a chemical affinityand a tendency to form hydroxides (for example Metal (OH)x), diamond anddiamond-like carbon.

(15) A low-friction lubrication assembly as described in any of (1) to(12), wherein the second member comprises at least one selected from thegroup consisting of C, Fe, Al, Mg, Cu, Fe alloy, Al alloy, Mg alloy andCu alloy.

(16) A low-friction lubrication assembly as described in any of (1) to(15), wherein the oxygen containing compound has at least one hydroxylgroup attached to the sliding surface.

(17) A low-friction lubrication assembly as described in any of (1) to(16), wherein the oxygen containing compound comprises at least one ofthe group consisting of an alcohol, a carboxylic acid, an ester, anether, a ketone, an aldehyde and a carbonate, and/or a derivative of atleast one of the group consisting of an alcohol, a carboxylic acid, anester, an ether, a ketone, an aldehyde and a carbonate.

(18) A supper low-friction lubrication assembly as described in any of(1) to (17), wherein the oxygen containing compound contains one or moreOH groups.

(19) A low-friction lubrication assembly as described in any of (1) to(17), wherein the oxygen containing compound comprises at least oneselected from the group consisting of poly alpha-olefin (PAO), glycerolmonooleate (GMO), Glycerol, H₂O and peroxides.

(20) A low-friction lubrication assembly as described in (1) to (19),wherein the oxygen containing compound comprises H₂O₂, a mixture of H₂Oand H₂O₂, or a mixture of H₂O₂ and glycerol.

(21) A low-friction lubrication assembly as described in any of (1) to(19), wherein the oxygen containing compound comprises polyalcohol.

(22) A low-friction lubrication assembly as described in (21), whereinthe polyalcohol comprises at least one selected from the groupconsisting of inositol, pyrogallol, urushiol, pyrocatechol, resorcinol,hydroquinone, fullerenol, penthaerythrithol, other saccharides, andtheir isomers, derivatives and substitution compounds.

(23) A low-friction lubrication assembly as described in (1) to (22),wherein the oxygen containing compound comprises a mixture of at leastone of the polyalcohols and glycerol.

(24) A low-friction lubrication assembly as described in (1) to (22),wherein the oxygen containing compound comprises a mixture of at leastone of the polyalcohols and H₂O.

(25) A low-friction lubrication assembly as described in any of (1) to(24), wherein the oxygen containing compound is found in synovialliquid.

(26) A low-friction lubrication assembly as described in any of (1) to(25), wherein the oxygen containing compound is found in lubricin.

(27) A low-friction lubrication assembly as described in any of (1) to(26), wherein the oxygen containing compound is found in lubricin-OH.

(28) A low-function lubrication assembly as described in (1) to (27),wherein the oxygen containing compound is liquid or gaseous,nanoparticles or thin organic deposited films by any availabledeposition techniques, in particular Langmuir Blodgett films.

(29) A low-friction lubrication assembly as described in any of (1) to(28), wherein the sliding surface of the first member is subject topretreatment before being slid against the second member.

(30) A low-friction lubrication assembly as described in any of (1) to(29), wherein the sliding surface of the second member is furthersubject to pretreatment before being slid against the first member.

(31) A low-friction lubrication assembly as described in (29) to (30),wherein said pretreatment comprises cleaning; mechanical activation, inparticular polishing; chemical treatment by application of the oxygencontaining compound; or physical treatment by laser treatment, ion beamtreatment or electron beam treatment.

(32) A supper low-friction lubrication assembly as described in (31),wherein the oxygen containing compound for carrying out the chemicaltreatment is high in volatility.

(33) A supper low-friction lubrication assembly as described in (32),wherein the oxygen containing compound high in volatility is H₂O₂.

(34) A low-friction lubrication assembly as described in any of (1) to(33), wherein the sliding surface of the first member is hydrogen-freebefore application of the oxygen containing compound and establishingsliding contact to the second member but comprises an OH-terminatedsliding surface upon entering into sliding contact with the secondmember, under preceding or simultaneous into application of the oxygencontaining compound on the sliding surface of the first member.

(35) A combustion engine, wherein the low-friction lubrication assemblyas described in (1) to (34) is applied to the combustion engine.

(36) A medical device, wherein the low-friction lubrication assembly asdescribed in (1) to (34) is applied to the medical device.

(37) A medical device as described in (36), wherein the medical deviceis endoscope, catheter, syringe, needle, blood collection tube, ormedical electronic pump.

(38) A shaver, wherein the low-friction lubrication assembly asdescribed in (1) to (34) is applied to the shaver.

(39) A watch, a compressor, a pump, a gear, a machining tool (bite) anda bearing, wherein the low-friction lubrication assembly as described in(1) to (34) is applied to the watch, the compressor, the pump, the gear,the machining tool and the bearing.

(40) A precision processing, wherein the low-friction lubricationassembly as described in (1) to (34) is applied to the precisionprocessing.

(41) A precision processing as described in (40), wherein the precisionprocessing is a cold processing or a warm processing.

(42) A precision instrument, wherein the low friction lubricationassembly as described in (1) to (34) is applied to the precisioninstrument.

(43) A watch to which a low-friction lubrication assembly is applied,wherein the low-friction lubrication assembly comprises: a first memberrelatively slidable against a second member, the first member havingchemical affinity with an OH-group on its sliding surface; and one ormore oxygen containing compounds located on the sliding surface of thefirst member and being able to produce a tribofilm to be located on thesliding surface of the first member having the chemical affinity,through hydrogen bond interactions with the OH-group.

(44) A watch as described in (43), wherein the second member further haschemical affinity with an OH group, and the tribofilm is also able to beformed on a sliding surface of the second member through hydrogen bondinteractions with the OH-group in response to sliding motion.

(45) A watch as described in (43), wherein at least one OH grouptermination is provided onto the sliding surface of the first memberafter a certain sliding motion.

(46) A watch as described in (43) or (45), wherein the tribofilm isformed to be located on the sliding surface of the first member throughhydrogen bond interactions between at least one OH termination providedto the surface of the first member and an OH group in the oxygencontaining compound.

(47) A watch as described in any of (43) to (46), wherein at least oneOH group termination is further provided onto the sliding surface of thesecond member after a certain sliding motion.

(48) A watch as described in any of (43) to (47), wherein the tribofilmis further formed to be located on the sliding surface of the secondmember through hydrogen bond interactions between at least one OHtermination provided to the surface of the second member and an OH groupin the oxygen containing compound.

(49) A watch as described in any of (43) to (48), wherein the firstmember contains at least Al₂O₃.

(50) A watch as described in any of (43) to (49), wherein the secondmember contains at least one selected from the group consisting of Feand Fe alloy.

(51) A watch as described in any of (43) to (50), wherein the oxygencontaining compound contains at least one selected from the groupconsisting of poly alpha-olefin (PAO), glycerol monooleate (GMO) andglycerol.

(52) A watch as described in any of (43) to (51), wherein the firstmember is made of Al₂O₃, the second member is made of Fe or Fe alloy,and the oxygen containing compound is glycerol.

(53) A watch as described in any of (43) to (52), wherein the firstmember made of Al₂O₃ is a fluke disposed in an anchor, and the secondmember made of Fe or Fe alloy is an escapement wheel.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 A schematic general outline of a low friction assembly beingformed of different first and second members.

FIG. 2 A schematic representation of the low friction assembly usingsimilar first and second members.

FIG. 3 A view representing a low friction assembly having a first and asecond member with an OH-terminated surface and a monolayer of glycerolas a lubricating agent on each surface. The spotted lines indicatehydrogen bonds and the sliding interface.

FIG. 4 A graph showing performances of a hydrogen-free DLC/hydrogen-freeDLC system with glycerol lubrication.

FIG. 5 A graph showing performances of a hydrogen-free/hydrogen-free DLCsystem with gaseous H₂O₂ lubrication.

FIG. 6 A schematic view showing a test condition of a vibration frictionwear testing machine (SRV sliding test).

FIG. 7 An explanatory illustration showing bonding between glycerol andta-C.

FIG. 8 A ternary state diagram showing ranges of ta-C and a-C.

FIG. 9 A graph showing performances of a ruby (Al₂O₃)/hydrogen-free DLCsystem with glycerol lubrication.

FIG. 10 A graph showing performances of a ruby (Al₂O₃)/hydrogen-free DLCsystem with PAO-ester lubrication.

FIG. 11 A graph showing performances of a ruby (Al₂O₃)/steel system withglycerol lubrication.

FIG. 12 A graph showing performances of a ruby (Al₂O₃)/steel system withPAO-ester lubrication.

FIG. 13 A graph showing a performance of a ruby (Al₂O₃)/steel systemusing glycerol containing 1% by weight of inositol as a lubricant.

What is claimed is:
 1. A watch comprising a low-friction lubricationassembly, characterized in that the low-friction lubrication assemblycomprises: a first member relatively slidable against a second member,the first member having chemical affinity with an OH-group on itssliding surface; and one or more oxygen containing compounds located onthe sliding surface of the first member and being able to produce atribofilm to be located on the sliding surface of the first memberhaving the chemical affinity, through hydrogen bond interactions withthe OH-group, wherein the first member includes a coating formed of adiamond-like carbon of ta-C type on its sliding surface, wherein the oneor more oxygen containing compounds include glycerol, wherein the secondmember has a chemical affinity with an OH-group on its sliding surface,and the tribofilm is able to be formed on the sliding surface of thesecond member through hydrogen bond interactions with the OH-group inresponse to a sliding motion of the first member against the secondmember, and wherein the second member includes a coating formed of adiamond-like carbon of the ta-C type on its sliding surface.
 2. Alow-friction lubrication assembly comprising: a first member relativelyslidable against a second member, the first member having chemicalaffinity with an OH-group on its sliding surface; and one or more oxygencontaining compounds located on the sliding surface of the first memberand being able to produce a tribofilm to be located on the slidingsurface of the first member having the chemical affinity, throughhydrogen bond interactions with the OH-group, wherein the first memberincludes a coating formed of a diamond-like carbon of ta-C type on itssliding surface, wherein the one or more oxygen containing compoundsinclude glycerol, wherein the second member has a chemical affinity withan OH-group on its sliding surface, and the tribofilm is able to beformed on the sliding surface of the second member through hydrogen bondinteractions with the OH-group in response to a sliding motion of thefirst member against the second member, wherein the second memberincludes a coating formed of a diamond-like carbon of the ta-C type onits sliding surface, and wherein the first member comprises at least oneselected from the group consisting of silicon carboxide, oxinitride andcarbonitride, a material formed of elements having a chemical affinityand tendency to form hydroxides, and diamond.
 3. A low-frictionlubrication assembly comprising: a first member relatively slidableagainst a second member, the first member having chemical affinity withan OH-group on its sliding surface; and one or more oxygen containingcompounds located on the sliding surface of the first member and beingable to produce a tribofilm to be located on the sliding surface of thefirst member having the chemical affinity, through hydrogen bondinteractions with the OH-group, wherein the first member includes acoating formed of a diamond-like carbon of ta-C type on its slidingsurface, wherein the one or more oxygen containing compounds includeglycerol, wherein the second member has a chemical affinity with anOH-group on its sliding surface, and the tribofilm is able to be formedon the sliding surface of the second member through hydrogen bondinteractions with the OH-group in response to a sliding motion of thefirst member against the second member, wherein the second memberincludes a coating formed of a diamond-like carbon of the ta-C type onits sliding surface, and wherein the second member comprises at leastone selected from the group consisting of silicon carboxide, oxinitrideand carbonitride, a material formed of elements having a chemicalaffinity and a tendency to form hydroxides, and diamond.